Death Sand

In the famous Smyth Report (Atomic Energy for Military Purposes) appears this ominous sentence: "The fission products produced in one day's run of a 100,000-kilowatt chain-reacting pile might be sufficient to make a large area uninhabitable." The Smyth Report appeared in 1945. Since then, "radiological poisons" have hardly been mentioned, much less evaluated publicly as a military weapon.

Why this silence? wonders Dr. Louis N. Ridenour, dean of the Graduate School of the University of Illinois, in the latest Bulletin of the Atomic Scientists. Are radiological poisons ineffective? Or are they so deadly that atom-minded governments have smothered all mention of them under blanket security?

To answer these questions, Ridenour turns to an article published in Vienna in 1948 by Austrian Physicist Hans Thirring. No possible breach of security here; Thirring had no information which was not available to all the world's physicists.

Curies & Roentgens. Dr. Thirring calculated that each 100 uranium atoms that fission in a pile produce 61 atoms useful as radioactive poisons; i.e., their half-lives are not less than eight days (which would make them become harmless too quickly) or more than a year (which would make them too mild initially).

The rate of reaction of a pile is measured in kilowatts, so Thirring calculates how much war-useful radioactivity could be produced per kilowatt. The answer comes out in curies, the unit of radioactivity, and Thirring figures that for each kilowatt a pile produces in a month 250 curies of radioactive poisons.

How deadly is a curie? Thirring starts with the assumption that 2,000 roentgens (the unit of radiation) will kill a man. After considering many factors, he concludes that a radioactive poison spread over the ground at the rate of two curies per square meter would give a man eight roentgens of radiation per hour. In about ten days this would build up to the lethal dose of 2,000 roentgens. The period of grace, thinks Ridenour, makes radiological poison a rather humane weapon. The inhabitants of a contaminated city could save their lives if they set out promptly.

A Ton for Manhattan. The U.S. chain-reacting piles at Hanford, Wash., Ridenour says, are now operating at a rate of at least 3,000,000 kilowatts. This means that the radioactive materials they produce in a month could contaminate (at the rate of two curies per square meter) about 144 square miles of territory. The area of Manhattan Island, Ridenour points out cheerfully, is slightly more than 22 square miles.

Thirring does not mention the difficulties of manufacturing and spreading the poison. He only suggests that it be mixed with powdered sand. This "death sand" (containing .05% of radioactive material) would be applied at a rate of 12 milligrams (1/2500 oz.) per square meter and would be entirely invisible. Less than a ton of death sand, evenly distributed, would make Manhattan a deathtrap.

"All in all," Ridenour concludes, "the official silence on radiological warfare probably is expressive of [military security] rather than disinterest."

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